[CRD iOS] Fix bugs in FlingTracker

remoting/client/ui/fling_tracker.h

 // Copyright 2017 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef REMOTING_CLIENT_UI_FLING_TRACKER_H_
 #define REMOTING_CLIENT_UI_FLING_TRACKER_H_
 
 #include "base/time/time.h"
 
 namespace remoting {
 
 // A class for tracking the positions of an object moving through a viscous
 // liquid.
 class FlingTracker {
  public:
-  // time_constant: The larger the number the longer it takes to fling.
+  // time_constant: The larger the number the longer it takes to fling and the
+  // further the object can move.
   explicit FlingTracker(float time_constant);
 
   ~FlingTracker();
 
   // Sets the position of the object and start fling. This will reset the
   // existing fling.
+  // |velocity_x| and |velocity_y| need to be in pixel per second.
   void StartFling(float velocity_x, float velocity_y);
 
   void StopFling();
 
   bool IsFlingInProgress() const;
 
   // time_elapsed: The time elapsed since the animation has started.
   // Moves forward the object to catch up with |time_elapsed|. The change in
   // positions will be written to |dx| and |dy|.
   // Returns true if the fling is still in progress at |time_elapsed|, false
   // otherwise, in which case |dx| and |dy| will not be touched.
   bool TrackMovement(base::TimeDelta time_elapsed, float* dx, float* dy);
 
  private:
   float time_constant_;
   float initial_speed_rate_ = 0.f;
+  float fling_duration_ = 0.f;
   float velocity_ratio_x_ = 0.f;
   float velocity_ratio_y_ = 0.f;
   float previous_position_x_ = 0.f;
   float previous_position_y_ = 0.f;
 
-  base::TimeTicks start_time_;
-
   // FlingTracker is neither copyable nor movable.
   FlingTracker(const FlingTracker&) = delete;
   FlingTracker& operator=(const FlingTracker&) = delete;
 };
 
 }  // namespace remoting
 #endif  // REMOTING_CLIENT_UI_FLING_TRACKER_H_